Heart valve replacement may be indicated when there is a narrowing of the native heart valve, commonly referred to as stenosis, or when the native valve leaks or regurgitates, such as when the leaflets are calcified. In one therapeutic solution, the native valve may be excised and replaced with either a biologic or a mechanical valve. Prosthetic valves attach to the patient's fibrous heart valve annulus, with or without the leaflets being present.
Conventional heart valve surgery is an open-heart procedure that is highly invasive, resulting in significant risks include bleeding, infection, stroke, heart attack, arrhythmia, renal failure, adverse reactions to the anesthesia medications, as well as sudden death. Fully 2-5% of patients die during surgery. The average hospital stay is between 1 to 2 weeks, with several more weeks to months required for complete recovery.
In recent years, advancements in “minimally-invasive” surgery and interventional cardiology have encouraged some investigators to pursue replacement of heart valves using remotely-implanted expandable valves without opening the chest or putting the patient on cardiopulmonary bypass. For instance, Percutaneous Valve Technologies (“PVT”) of Fort Lee, N.J. and Edwards Lifesciences of Irvine, Calif., have developed a balloon-expandable stent integrated with a bioprosthetic valve. The stent/valve device is deployed across the native diseased valve to permanently hold the valve open, thereby alleviating a need to excise the native valve. PVT's device is designed for percutaneous delivery in a cardiac catheterization laboratory under local anesthesia using fluoroscopic guidance, thereby avoiding general anesthesia and open-heart surgery. Other percutaneously- or surgically-delivered expandable valves are also being tested. For the purpose of inclusivity, the entire field will be denoted herein as the delivery and implantation of expandable valves.
Expandable heart valves use either balloon-or self-expanding stents as anchors. In an aortic valve replacement procedure in particular, accurate placement of the prosthetic valve relative to the annulus and coronary ostia is important. Perhaps more critical, the uniformity of contact between the expandable valve and surrounding annulus, with or without leaflets, should be such that no paravalvular leakage occurs. This is sometimes difficult given the highly calcified condition of the aortic annulus in particular. Furthermore, due to the remote nature of expandable valve replacement procedures, the physician does not have the luxury of carefully positioning and then securing the periphery of the valve to the annulus with sutures, as with conventional open-heart techniques. Therefore, some have proposed various means for sealing the valve against the annulus, including providing sacs filled with sealing material around the exterior of the valve as in U.S. Patent Publication No. 2005-0137687 to Salahieh, et al. Other techniques for detecting leaks and/or sealing around expandable valves are disclosed in Spenser, et al., U.S. Patent Publication No. 2006-0004442.
Short of clinical trials, animal models (i.e., ovine and porcine) have been used in an attempt to evaluate the paravalvular and migration performance of both minimally invasive surgical (MIS) and percutaneous aortic valves. However, the animals used are typically healthy specimens whose heart valves are unlike the calcified or otherwise distorted annuluses of the typical prosthetic valve recipient. Implantation training is often done using animal models as well.
Due to the intense current interest in expandable prosthetic heart valves, there is a need for a better means for ensuring the efficacy of these valves and for training physicians in the new techniques of implantation.